Social media apps use your phone number to triangulate data such as purchase history, not to help you with two factor authentication or account security. Please LinkedIn. No you can't have my phone number.

Some folks don't agree (tweet).

In 2015 I warned people that LinkedIn was mining user data (contacts, calendars, etc.):

How to Manage LinkedIn Privacy – Stop Sharing Your Contacts

News article:

Now Facebook is allowing anyone to look you up using your security phone number - Fast Company 3/4/2019

Music credit:

Hall and Oates - "Private Eyes"